Systems and methods for implanting electrode leads for use with implantable neuromuscular electrical stimulator

ABSTRACT

A system of implanting electrode leads for restoring muscle function to the lumbar spine to treat low back pain is provided. The system provides efficient implantation of the leads, including the ability to verify deployment of anchoring mechanisms on the lead using an impedance assessment, such that the implanted lead may be secured within the patient and used to restore muscle function of local segmental muscles associated with the lumbar spine stabilization system.

I. CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part application of U.S. patentapplication Ser. No. 14/061,614, filed Oct. 23, 2013, the entirecontents of which is incorporated herein by reference. This applicationis also a continuation-in-part application of U.S. patent applicationSer. No. 13/797,100, filed Mar. 12, 2013, which claims the benefit ofpriority of U.S. Provisional Application Ser. No. 61/659,334, filed Jun.13, 2012, the entire contents of each of which is incorporated herein byreference.

II. FIELD OF THE INVENTION

This application generally relates to systems and methods for implantingelectrode leads for neuromuscular electrical stimulation, includingstimulation of tissue associated with control of the lumbar spine fortreatment of back pain.

III. BACKGROUND OF THE INVENTION

The human back is a complicated structure including bones, muscles,ligaments, tendons, nerves and other structures. The spinal column hasinterleaved vertebral bodies and intervertebral discs, and permitsmotion in several planes including flexion-extension, lateral bending,axial rotation, longitudinal axial distraction-compression,anterior-posterior sagittal translation, and left-right horizontaltranslation. The spine provides connection points for a complexcollection of muscles that are subject to both voluntary and involuntarycontrol.

Back pain in the lower or lumbar region of the back is common. In manycases, the cause of back pain is unknown. It is believed that some casesof back pain are caused by abnormal mechanics of the spinal column.Degenerative changes, injury of the ligaments, acute trauma, orrepetitive microtrauma may lead to back pain via inflammation,biochemical and nutritional changes, immunological factors, changes inthe structure or material of the endplates or discs, and pathology ofneural structures.

The spinal stabilization system may be conceptualized to include threesubsystems: 1) the spinal column, which provides intrinsic mechanicalstability; 2) the spinal muscles, which surround the spinal column andprovide dynamic stability; and 3) the neuromotor control unit, whichevaluates and determines requirements for stability via a coordinatedmuscle response. In patients with a functional stabilization system,these three subsystems work together to provide mechanical stability. Itis applicant's realization that low back pain results from dysfunctionof these subsystems.

The spinal column consists of vertebrae and ligaments, e.g. spinalligaments, disc annulus, and facet capsules. There has been an abundanceof in-vitro work in explanted cadaver spines and models evaluating therelative contribution of various spinal column structures to stability,and how compromise of a specific column structure will lead to changesin the range of motion of spinal motion segments.

The spinal column also has a transducer function, to generate signalsdescribing spinal posture, motions, and loads via mechanoreceptorspresent in the ligaments, facet capsules, disc annulus, and otherconnective tissues. These mechanoreceptors provide information to theneuromuscular control unit, which generates muscle response patterns toactivate and coordinate the spinal muscles to provide muscle mechanicalstability. Ligament injury, fatigue, and viscoelastic creep may corruptsignal transduction. If spinal column structure is compromised, due toinjury, degeneration, or viscoelastic creep, then muscular stabilitymust be increased to compensate and maintain stability.

Muscles provide mechanical stability to the spinal column. This isapparent by viewing cross section images of the spine, as the total areaof the cross sections of the muscles surrounding the spinal column islarger than the spinal column itself. Additionally, the muscles havemuch larger lever arms than those of the intervertebral disc andligaments.

Under normal circumstances, the mechanoreceptors exchange signals withthe neuromuscular control unit for interpretation and action. Theneuromuscular control unit produces a muscle response pattern based uponseveral factors, including the need for spinal stability, posturalcontrol, balance, and stress reduction on various spinal components.

It is believed that in some patients with back pain, the spinalstabilization system is dysfunctional. With soft tissue injury,mechanoreceptors may produce corrupted signals about vertebral position,motion, or loads, leading to an inappropriate muscle response. Inaddition, muscles themselves may be injured, fatigued, atrophied, orlose their strength, thus aggravating dysfunction of the spinalstabilization system. Conversely, muscles can disrupt the spinalstabilization system by going into spasm, contracting when they shouldremain inactive, or contracting out of sequence with other muscles. Asmuscles participate in the feedback loop via mechanoreceptors in theform of muscle spindles and golgi tendon organs, muscle dysfunction mayfurther compromise normal muscle activation patterns via the feedbackloops.

Trunk muscles may be categorized into local and global muscles. Thelocal muscle system includes deep muscles, and portions of some musclesthat have their origin or insertion on the vertebrae. These localmuscles control the stiffness and intervertebral relationship of thespinal segments. They provide an efficient mechanism to fine-tune thecontrol of intervertebral motion. The lumbar multifidus, with itsvertebra-to-vertebra attachments is an example of a muscle of the localsystem. Another example is the transverse abdominus, with its directattachments to the lumbar vertebrae through the thoracolumbar fascia.

The multifidus is the largest and most medial of the lumbar backmuscles. It has a repeating series of fascicles which stem from thelaminae and spinous processes of the vertebrae, and exhibit a constantpattern of attachments caudally. These fascicles are arranged in fiveoverlapping groups such that each of the five lumbar vertebrae givesrise to one of these groups. At each segmental level, a fascicle arisesfrom the base and caudolateral edge of the spinous process, and severalfascicles arise, by way of a common tendon, from the caudal tip of thespinous process. Although confluent with one another at their origin,the fascicles in each group diverge caudally to assume separateattachments to the mamillary processes, the iliac crest, and the sacrum.Some of the deep fibers of the fascicles that attach to the mamillaryprocesses attach to the capsules of the facet joints next to themamillary processes. The fasicles arriving from the spinous process of agiven vertebra are innervated by the medial branch of the dorsal ramusthat issues from below that vertebra.

The global muscle system encompasses the large, superficial muscles ofthe trunk that cross multiple motion segments, and do not have directattachment to the vertebrae. These muscles are the torque generators forspinal motion, and control spinal orientation, balance the externalloads applied to the trunk, and transfer load from the thorax to thepelvis. Global muscles include the oblique internus abdominus, theobliquus externus abdmonimus, the rectus abdominus, the lateral fibersof the quadratus lumborum, and portions of the erector spinae.

Normally, load transmission is painless. Over time, dysfunction of thespinal stabilization system is believed to lead to instability,resulting in overloading of structures when the spine moves beyond itsneutral zone. The neutral zone is a range of intervertebral motion,measured from a neutral position, within which the spinal motion isproduced with a minimal internal resistance. High loads can lead toinflammation, disc degeneration, facet joint degeneration, and musclefatigue. Since the endplates and annulus have a rich nerve supply, it isbelieved that abnormally high loads may be a cause of pain. Loadtransmission to the facets also may change with degenerative discdisease, leading to facet arthritis and facet pain.

For patients believed to have back pain due to instability, cliniciansoffer treatments intended to reduce intervertebral motion. Commonmethods of attempting to improve muscle strength and control includecore abdominal exercises, use of a stability ball, and Pilates. Spinalfusion is the standard surgical treatment for chronic back pain.Following fusion, motion is reduced across the vertebral motion segment.Dynamic stabilization implants are intended to reduce abnormal motionand load transmission of a spinal motion segment, without fusion.Categories of dynamic stabilizers include interspinous process devices,interspinous ligament devices, and pedicle screw-based structures. Totaldisc replacement and artificial nucleus prostheses also aim to improvespine stability and load transmission while preserving motion.

There are a number of problems associated with current implants that aimto restore spine stabilization. First, it is difficult to achieveuniform load sharing during the entire range of motion if the locationof the optimum instant axis of rotation is not close to that of themotion segment during the entire range of motion. Second, cyclic loadingof dynamic stabilization implants may cause fatigue failure of theimplant, or the implant-bone junction, e.g. screw loosening. Third,implantation of these systems requires surgery, which may cause new painfrom adhesions, or neuroma formation. Moreover, surgery typicallyinvolves cutting or stripping ligaments, capsules, muscles, and nerveloops, which may interfere with the spinal stabilization system.

Functional electrical stimulation (FES) is the application of electricalstimulation to cause muscle contraction to re-animate limbs followingdamage to the nervous system such as with stroke or spine injury. FEShas been the subject of much prior art and scientific publications. InFES, the goal generally is to bypass the damaged nervous system andprovide electrical stimulation to nerves or muscles directly whichsimulates the action of the nervous system. One lofty goal of FES is toenable paralyzed people to walk again, and that requires the coordinatedaction of several muscles activating several joints. The challenges ofFES relate to graduation of force generated by the stimulated muscles,and the control system for each muscle as well as the system as a wholeto produce the desired action such as standing and walking.

With normal physiology, sensors in the muscle, ligaments, tendons andother anatomical structures provide information such as the force amuscle is exerting or the position of a joint, and that information maybe used in the normal physiological control system for limb position andmuscle force. This sense is referred to as proprioception. In patientswith spinal cord injury, the sensory nervous system is usually damagedas well as the motor system, and thus the afflicted person losesproprioception of what the muscle and limbs are doing. FES systems oftenseek to reproduce or simulate the damaged proprioceptive system withother sensors attached to a joint or muscle.

Neuromuscular Electrical Stimulation (NMES) is a subset of the generalfield of electrical stimulation for muscle contraction, as it isgenerally applied to nerves and muscles which are anatomically intact,but malfunctioning is a different way. NMES may be delivered via anexternal system or, in some applications, via an implanted system.

The goals and challenges of rehabilitation of anatomically intact (i.e.,non-pathological) neuromuscular systems are fundamentally different fromthe goals and challenges of FES for treating spinal injury patients orpeople suffering from spasticity. In muscle rehabilitation, the primarygoal is to restore normal functioning of the anatomically intactneuromuscular system, whereas in spinal injury and spasticity, theprimary goal is to simulate normal activity of a pathologically damagedneuromuscular system.

U.S. Pat. Nos. 8,428,728 and 8,606,358 to Sachs, both assigned to theassignee of the present invention, and both incorporated herein in theirentireties by reference, describe implanted electrical stimulationdevices that are designed to restore neural drive and rehabilitate themultifidus muscle to improve stability of the spine. Rather than maskingpain signals while the patient's spinal stability potentially undergoesfurther deterioration, the stimulator systems described in thoseapplications are designed to reactivate the motor control system and/orstrengthen the muscles that stabilize the spinal column, which in turnis expected to reduce persistent or recurrent pain.

While the stimulator systems described in the Sachs patents seek torehabilitate the multifidus and restore neural drive, use of thosesystems necessitates the implantation of one or more electrode leads inthe vicinity of a predetermined anatomical site, such as the medialbranch of the dorsal ramus of the spinal nerve to elicit contraction ofthe lumbar multifidus muscle. For lead implantation using the Seldingertechnique, it has been proposed to insert a needle in the patient'sback, insert a guidewire through a lumen in the needle, remove theneedle, insert a sheath over the guidewire, remove the guidewire, insertthe electrode lead through a lumen of the sheath, and remove the sheath.Such a process requires many instruments and can be quite timeconsuming.

It would therefore be desirable to provide systems and methods forimplanting an electrode lead in a more efficient manner.

IV. SUMMARY OF THE INVENTION

The present invention overcomes the drawbacks of previously-knownsystems by providing systems and methods for implanting an electrodelead. The lead may be configured to restore muscle function to thelumbar spine to treat, for example, low back pain. The systems andmethods are expected to provide efficient implantation of the lead,including the ability to verify deployment of anchoring mechanisms onthe lead based on impedance measurements, such that the implanted leadmay be secured within the patient and used to restore muscle function oflocal segmental muscles associated with the lumbar spine stabilizationsystem.

In accordance with one aspect, a system for restoring muscle function tothe lumbar spine is provided. The system may include first and secondelectrodes configured to be implanted in or adjacent to tissueassociated with control of the lumbar spine, a lead having the first andsecond electrodes disposed thereon, a fixation element coupled to thelead and disposed in proximity to the first electrode, a pulse generatorcoupled to the first and second electrodes via the lead, and softwarestored on a non-transient computer readable media configured to run onan external computer operatively coupled to the pulse generator. Thefixation element may be configured to transition from a delivery state,wherein the fixation element is positioned adjacent to the firstelectrode, to a deployed state, wherein the fixation element is spacedapart from the first electrode and is positioned to anchor the lead toan anchor site, e.g., muscle. The pulse generator may be configured tocause the first or second electrode to emit energy such that the secondor first electrode, respectively, receives a portion of the emittedenergy. The pulse generator may be further configured to transmit asignal indicative of an impedance measurement based on the energyemitted (e.g., from the first or second electrode) and the portion ofthe energy received (e.g., at the second or first electrode). Thesoftware may be configured to cause the external computer to display theimpedance measurement indicative of whether the fixation element is inthe delivery state or the deployed state.

The system may further include a second fixation element coupled to thelead distal to the fixation element, wherein the fixation element isangled distally relative to the lead and the second fixation element isangled proximally relative to the lead. The fixation element and thesecond fixation element may be configured to sandwich the anchor sitetherebetween.

The system also may include an external programmer coupled to theexternal computer, where the external programmer is configured toreceive the signal indicative of the impedance measurement from thepulse generator and to transmit the signal to the external computer. Inaddition, the external programmer may be configured to transferprogramming data to the pulse generator. The software may be configuredto permit selection, adjustment, and display of the programming data.The programming data may include at least one of: pulse amplitude, pulsewidth, stimulation rate, stimulation frequency, ramp timing, cycletiming, session timing, or electrode configuration. The software may beconfigured to determine whether the fixation element is in the deliverystate or the deployed state.

The system further may include a handheld activator configured totransfer a stimulation command to the pulse generator, wherein thestimulation command directs at least one of the first or secondelectrodes to stimulate the tissue in accordance with the programmingdata.

The software may be configured to cause the external computer to displaya second impedance measurement based on a second signal. The impedancemeasurement and the second impedance measurement may be compared, e.g.,by a physician or by the software, to determine whether the fixationelement is in the delivery state or the deployed state. In oneembodiment, the impedance measurement is indicative of the fixationelement being in the delivery state in a range; e.g., between 1501-3500ohms, 1200-2500 ohms, 1000-2000 ohms, or 750-1750 ohms; and theimpedance measurement is indicative of the fixation element being in thedeployed state in a different range; e.g., between 500-1500 ohms,500-1200 ohms, 500-1000 ohms, or 500-750 ohms. Also, the lead may beconfigured to be delivered through a sheath.

In accordance with another aspect, a method of verifying deployment of afixation element in a system for restoring muscle function to the lumbarspine is provided. The method may include implanting a lead such that anelectrode disposed on the lead is positioned in or adjacent to tissueassociated with control of the lumbar spine, the lead coupled to afixation element disposed in proximity to the electrode, the fixationelement configured to transition from a delivery state, wherein thefixation element is positioned adjacent to the electrode, to a deployedstate, wherein the fixation element is spaced apart from the electrodeand is positioned to anchor the lead to an anchor site; causing theelectrode to stimulate tissue using a pulse generator; transmitting asignal indicative of an impedance measurement to an external display;displaying the impedance measurement on the external display; anddetermining whether the fixation element is in the delivery state or thedeployed state based on the displayed impedance measurement.

The signal may be transmitted from the pulse generator to an externalprogrammer coupled to an external computer having the external display.The method may further include adjusting the lead if the fixationelement is determined to be in the delivery state.

In accordance with yet another aspect, a kit for implanting an electrodelead in a system for restoring muscle function to the lumbar spine isprovided. The kit may include a sheath configured for insertion in alower back of a patient, a needle electrode, and a lead having anelectrode at a distal end of the lead. The sheath has a lumen extendingtherethrough. The needle electrode has a distal end configured to bepositioned in or adjacent to tissue associated with control of thelumbar spine through the lumen. The needle electrode may be configuredto stimulate the tissue to permit verification of needle electrodepositioning. The lead may be configured for implantation through thelumen to position the electrode in or adjacent to the tissue associatedwith control of the lumbar spine.

The sheath may include a window and the needle electrode may beconfigured to stimulate the tissue through the window. The kit mayfurther include an implantable pulse generator configured to be coupledto the electrode via the lead.

In accordance with another aspect, a method of implanting an electrodelead is provided. The method may include inserting a needle electrodedisposed within a lumen of a sheath into a patient such that a distalend of the needle electrode is positioned in or adjacent to tissueassociated with control of the lumbar spine; stimulating the tissue withthe needle electrode; verifying placement of the distal end of theneedle electrode at the tissue; removing the needle electrode from thesheath; inserting an electrode lead through the lumen of the sheath suchthat an electrode disposed on the lead is implanted in or adjacent tothe tissue associated with control of the lumbar spine; and removing thesheath. Advantageously, a guidewire need not be used for inserting theneedle electrode or inserting the electrode lead. The method may furtherinclude stimulating the tissue with the electrode to rehabilitatefunction of a multifidus muscle and improve spinal stability.

V. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an exemplary embodiment of a stimulatorsystem constructed in accordance with the principles of the presentinvention.

FIGS. 2A and 2B show an exemplary electrode lead of the stimulatorsystem of FIG. 1, wherein fixation elements of the lead are shown in adelivery state in FIG. 2A and in a deployed state in FIG. 2B.

FIG. 3 shows a generalized block diagram of an exemplary implantablepulse generator (IPG) of the stimulator system of FIG. 1.

FIG. 4 shows an exemplary kit for delivering the electrode lead of thestimulator system of FIG. 1.

FIG. 5 shows a generalized block diagram of an exemplary circuitryhousing that may be used together with the needle electrode of the kitof FIG. 4.

FIGS. 6A through 6F show an exemplary method for implanting theelectrode lead of the stimulator system of FIG. 1 using the kit of FIG.4.

FIG. 7 is an exemplary screenshot illustrating various aspects of thegraphical user interface of the software-based programming system of thepresent invention.

VI. DETAILED DESCRIPTION OF THE INVENTION

The neuromuscular stimulation system of the present invention comprisesimplantable devices for facilitating electrical stimulation to tissuewithin a patient's back and external devices for wirelesslycommunicating programming data and stimulation commands to theimplantable devices. The devices disclosed herein may be utilized tostimulate tissue associated with local segmental control of the lumbarspine in accordance with the programming data to rehabilitate the tissueover time. In accordance with the principles of the present invention,the stimulator system may be optimized for use in treating back pain inthe region of the lumbar spine.

Provided herein are systems and methods for implanting an electrodelead(s) of the neuromuscular stimulation system. The systems and methodsare expected to provide efficient implantation of the lead, includingthe ability to verify deployment of anchoring mechanisms on the lead,such that the implanted lead may be secured within the patient.

Referring to FIG. 1, an overview of an exemplary stimulator systemconstructed in accordance with the principles of the present inventionis provided. In FIG. 1, components of the system are not depicted toscale on either a relative or absolute basis. Stimulator system 100 mayinclude electrode lead 200, implantable pulse generator (IPG) 300,activator 400, optional magnet 450, external programmer 500, andsoftware-based programming system 600.

Electrode lead 200 includes lead body 202 having a plurality ofelectrodes, illustratively, electrodes 204, 206, 208, and 210. Electrodelead 200 is configured for implantation in or adjacent to tissue, e.g.,nervous tissue, muscle, a ligament, and/or a joint capsule, includingtissue associated with local segmental control of the lumbar spine.Electrode lead 200 is coupled to IPG 300, for example, via connectorblock 302. IPG 300 is configured to generate pulses such that electrodes204, 206, 208, and/or 210 deliver neuromuscular electrical stimulation(“NMES”) to target tissue. In one embodiment, the electrodes arepositioned to stimulate a peripheral nerve where the nerve entersskeletal muscle, which may be one or more of the multifidus, transverseabdominus, quadratus lumborum, psoas major, internus abdominus, obliquusexternus abdominus, and erector spinae muscles. Such stimulation mayinduce contraction of the muscle to restore neural control andrehabilitate the muscle, thereby improving muscle function of localsegmental muscles of the lumbar spine, improving lumbar spine stability,and reducing back pain.

IPG 300 may be controlled by, and optionally powered by, activator 400,which includes control module 402 coupled to pad 404, e.g., via cable406. Control module 402 has user interface 408 that permits a user,e.g., patient, physician, caregiver, to adjust a limited number ofoperational parameters of IPG 300 including starting and stopping atreatment session. Control module 402 communicates with IPG 300 via pad404, which may comprise an inductive coil or RF transceiver configuredto communicate information in a bidirectional manner across a patient'sskin to IPG 300 and, optionally, to transmit power to IPG 300. Forexample, a controller within control module 402 may send a stimulationcommand(s) responsive to user input received at user interface 408 to acontroller of IPG 300 via respective telemetry (or RF) systems inactivator 400 and IPG 300. The stimulation commands may include, forexample, at least one of: a command to start a treatment session or stopthe treatment session; a command to provide a status of IPG 300; or arequest to conduct an impedance assessment. In a preferred embodiment, alimited number of stimulation parameters may be adjusted at userinterface 408 to minimize the chance of injury caused by adjustmentsmade by non-physician users. In an alternative embodiment, thecontroller of activator 400 also may send adjustments to stimulationparameters, e.g., pulse amplitude (voltage or current), pulse width,stimulation rate, stimulation frequency, ramp timing, cycle timing,session timing, and electrode configuration to IPG 300 responsive touser input received at user interface 408.

Stimulator system 100 also may include optional magnet 450 configured totransmit a magnetic field across a patient's skin to IPG 300 such that amagnetic sensor of IPG 300 senses the magnetic field and IPG 300 startsor stops a treatment session responsive to the sensed magnetic field.

In FIG. 1, software-based programming system 600 is installed and runson a computer, e.g., conventional laptop, and is used by the patient'sphysician together with external programmer 500 to provide programmingto IPG 300. During patient visits, external programmer 500 may becoupled, either wirelessly or using a cable such as cable 502, to thephysician's computer such that software-based programming system 600 maydownload for review data stored on IPG 300 via external programmer 500.Software-based programming system 600 also may transfer programming datato IPG 300 via external programmer 500 to reprogram stimulationparameters programmed into IPG 300. For example, programming system 600may be used to program and adjust parameters such as pulse amplitude(voltage or current), pulse width, stimulation rate, stimulationfrequency, ramp timing, cycle timing, session timing, and electrodeconfiguration. Programming system 600 also may be configured to uploadand store data retrieved from IPG 300 to a remote server for lateraccess by the physician. Programming system 600 may be configured tocause the computer to display an impedance measurement taken atelectrode lead 200 and transmitted by IPG 300. The impedance measurementmay be used to determine whether the fixation element(s) on electrodelead 200 are in the delivered state or the deployed state, as describedin detail below.

Referring now to FIGS. 2A and 2B, an exemplary embodiment of electrodelead 200 is described. Electrode lead 200 contains a plurality ofelectrodes 204, 206, 208, and 210, disposed at distal end 211 of leadbody 202, that are configured to be implanted in or adjacent to tissue,such as nervous tissue, muscle, ligament, and/or joint capsule. Leadbody 202 is a suitable length for positioning the electrodes in oradjacent to target tissue while IPG is implanted in a suitable location,e.g., the lower back. For example, lead body 202 may be between about 30and 80 cm in length, and preferably about 45 or about 65 cm in length.Lead body 202 is also of a suitable diameter for placement, for example,between about 1 and 2 mm in diameter and preferably about 1.3 mm.Electrodes 204, 206, 208, and 210 may be configured to stimulate thetissue at a stimulation frequency and at a level and duration sufficientto cause muscle to contract and may be ring electrodes, partialelectrodes, segmented electrodes, nerve cuff electrodes placed aroundthe nerve innervating the target muscle, or the like. Electrodes 204,206, 208, 210 are a suitable length(s) and spaced apart a suitabledistance along lead body 202. For example, electrodes 204, 206, 208, 210may be about 2-5 mm in length, and preferably about 3 mm, and may bespaced apart about 2-6 mm, and preferably about 4 mm. As will also beunderstood by one of skill in the art, an electrode lead may containmore or fewer than four electrodes.

Also at distal end 211, fixation elements 212 and 213 may be coupled tolead body 202 via fixation ring 216 and fixation elements 214 and 215may be coupled to lead body 202 via fixation ring 218. Fixation elements212, 213, 214, 215 are shown in a delivery state in FIG. 2A, whereinfixation elements 212, 213, 214, 215 are positioned adjacent toelectrode 210, and are shown in a deployed state in FIG. 2B, whereinfixation elements 212, 213, 214, 215 are spaced apart from electrode 210and positioned to anchor lead 200 to an anchor site, e.g., muscle.

Fixation elements 212, 213, 214, 215 are configured to collapse inwardtoward lead body 202 in the delivery state, shown in FIG. 2A, and maycontact electrode 210 in the delivery state. In the illustratedembodiment, the longitudinal axis of each fixation element 212, 213,214, 215, when collapsed, is approximately parallel to the longitudinalaxis of lead 200 at distal end 211. In addition, fixation elements 212,213, 214, 215 may be sized such that the outer surface of each fixationelement 212, 213, 214, 215 aligns with the outer surface of fixationrings 216 and 218 to minimize catching of fixation elements 212, 213,214, 215 when delivered through a sheath. In the delivery state,fixation elements 212, 213, 214, 215 may at least partially coverportions of, or substantially all of, electrode 210. Advantageously, theclose proximity of fixation elements 212, 213, 214, 215 to electrode 210in the delivery state may be utilized to determine whether fixationelements 212, 213, 214, 215 have deployed during delivery because theimpedance at electrode 210 is different when fixation elements 212, 213,214, 215 are deployed as compared to when fixation elements 212, 213,214, 215 are collapsed adjacent to electrode 210.

Referring now to FIG. 2B, fixation elements 212, 213, 214, 215 areconfigured to self-expand, e.g., due to retraction of a sheath, in thedeployed state. Illustratively, fixation elements 212, 213, 214, 215 arespaced apart from electrode 210 at an angle suitable for anchoring lead200 to the anchor site. Preferably, in the deployed state, the anglebetween each fixation element 212, 213, 214, 215 and the longitudinalaxis of lead 200 at distal end 211 is between about 10-90 degrees, 20-80degrees, 25-70 degrees, 30-60 degrees, or 35-55 degrees, and preferablyabout 45 degrees. As will be readily understood, the angle between eachfixation element 212, 213, 214, 215 and the longitudinal axis of lead200 at distal end 211 need not be the same, and most likely will bedifferent as each fixation element 212, 213, 214, 215 expandsindividually through tissue.

Fixation elements 212 and 214 are configured to sandwich an anchor site,e.g., muscle, therebetween to secure electrode lead 200 at a target sitewithout damaging the anchor site. Likewise, fixation elements 213 and215 are configured to sandwich the same or a different anchor sitetherebetween to secure electrode lead 200 at the target site withoutdamaging that anchor site. Fixation elements 212 and 213 may be angleddistally relative to lead body 202, and resist motion in a firstdirection and prevent, in the case illustrated, insertion of the leadtoo far, as well as migration distally. Fixation element 212 may bedisposed opposite from fixation element 213, as illustrated. Fixationelements 214 and 215 are angled proximally relative to lead body 202 andpenetrate through a tissue plane and deploy on the distal side of thetissue immediately adjacent to a target of stimulation. Fixation element214 may be disposed opposite from fixation element 215, as illustrated.As will be understood by one of skill in the art, an electrode lead maycontain more or fewer than four fixation elements.

Fixation elements 212 and 213 are configured to resist motion in theopposite direction relative to fixation elements 214 and 215. Thiscombination prevents migration both proximally and distally, and also inrotation. In the illustrated embodiment, fixation elements 212 and 213are coupled to lead body 202 between electrode 208 and distal mostelectrode 210 and fixation elements 214 and 215 are coupled to lead body202 between distal most electrode 210 and end cap 220.

Fixation elements 212, 213, 214, 215 are preferably made from anonconductive material, e.g., a nonconductive polymer, and have agenerally rectangular cuboid shape, although the disclosure is notlimited thereto and other shapes may be utilized such as curved shapesand hooks. The nonconductive material may be used to ensure thatimpedance at electrode lead 200 will be different between the deliveryand the deployed states because the nonconductive material, whencontacting or immediately adjacent to electrode 210 in the deliverystate, will alter diffusion of energy to/from electrode 210 as comparedto when the nonconductive material is spaced apart from electrode 210 inthe deployed state. A measurement of the impedance may be used todetermine how many fixation elements 212, 213, 214, 215 have deployed,as fixation elements 212, 213, 214, 215 are independently deployable.For example, an impedance measurement within a first range, e.g.,between 1501-3500 ohms, may be indicative of fixation elements 212, 213,214, 215 being in the delivery state and an impedance measurement withina second range, e.g., between 500-1500 ohms, different from the firstrange, may be indicative of fixation elements 212, 213, 214, 215 beingin the deployed state. In addition, an impedance measurement within athird range, e.g., 1200-2500 ohms, different from the first and secondranges, may be indicative of one of fixation elements 212, 213, 214, 215being in the deployed state while the remaining fixation elements are inthe delivery state. Also, an impedance measurement within a fourthrange, e.g., 1000-2000 ohms, different from the first, second, and thirdranges, may be indicative of two of fixation elements 212, 213, 214, 215being in the deployed state while the remaining fixation elements are inthe delivery state. And an impedance measurement within a fifth range,e.g., 750-1750 ohms, different from the first, second, third, and fourthranges, may be indicative of three of fixation elements 212, 213, 214,215 being in the deployed state while the remaining fixation elementsare in the delivery state.

The length of and spacing between the fixation elements is defined bythe structure around which they are to be placed. In one embodiment, thelength of each fixation element is between about 1.5-4 mm and preferablyabout 2.5 mm and the spacing is between about 2 mm and 10 mm andpreferably about 6 mm.

While FIGS. 2A and 2B illustrate fixation elements 212, 213, 214, 215 onlead body 202, it should be understood that other fixation elements maybe used to anchor electrode lead 200 at a suitable location includingthe fixation elements described in U.S. Patent Application Pub. Nos.2013/0131766 to Crosby and 2013/0338730 to Shiroff, both assigned to theassignee of the present invention, the entire contents of each of whichis incorporated herein by reference.

Lead body 202 further may include stylet lumen 222 extendingtherethrough. Stylet lumen 222 is shaped and sized to permit a stylet tobe inserted therein, for example, during delivery of electrode lead 200.In one embodiment, end cap 220 is used to prevent the stylet fromextending distally out of stylet lumen 222 beyond end cap 220. Inaddition, end cap 220 may include a suitable coupling mechanism, e.g.,threads, for coupling to the stylet such that the stylet is temporarilylocked to end cap 220.

At proximal end 224, electrode lead 200 includes contacts 226, 228, 230,and 232 separated along lead body 202 by spacers 234, 236, 238, 240, and242. Contacts 226, 228, 230, and 232 may comprise an isodiametricterminal and are electrically coupled to electrodes 204, 206, 208, and210, respectively, via, for example, individually coated spiral woundwires. A portion of proximal end 224 is configured to be inserted in IPG300 and set-screw retainer 244 is configured to receive a screw from IPG300 to secure the portion of electrode lead 200 within IPG 300.

As would be apparent to one of ordinary skill in the art, variouselectrode locations and configurations would be acceptable, includingthe possibility of skin surface electrodes. The electrode(s) may be anarray of a plurality of electrodes, or may be a simple single electrodewhere the electrical circuit is completed with an electrode placedelsewhere (not shown) such as a skin surface patch or by the can of animplanted pulse generator. In addition, electrode lead 200 may comprisea wirelessly activated or leadless electrode, such as described in U.S.Pat. No. 8,321,021 to Kisker, such that no lead need be coupled to IPG300.

With respect to FIG. 3, a generalized schematic diagram of the internalfunctional components of IPG 300 is now described. IPG 300 is configuredto cause the electrodes to stimulate in accordance with programming datastored in the memory of IPG 300. IPG 300 may include programmablecontroller 318, communication unit 320, power supply 324, electrodeswitching array 326, system sensors 328, and optional therapeuticcircuitry module 330.

Controller 318 is electrically coupled to, and configured to control,the internal functional components of IPG 300. Controller 318 maycomprise a commercially available microcontroller unit including aprogrammable microprocessor, volatile memory, nonvolatile memory such asEEPROM for storing programming, and nonvolatile storage, e.g., Flashmemory, for storing firmware and a log of system operational parametersand patient data. The memory of controller 318 stores programinstructions that, when executed by the processor of controller 318,cause the processor and the functional components of IPG 300 to providethe functionality ascribed to them herein. Controller 318 is configuredto be programmable such that programming data is stored in the memory ofcontroller 318 and may be adjusted using external programmer 500 asdescribed in detail in U.S. Patent Pub. No. 2014/0046398 to Sachs, theentire contents of which is incorporated herein by reference.Programming data may include pulse amplitude (voltage or current), pulsewidth, stimulation rate, stimulation frequency, ramp timing, cycletiming, session timing, and electrode configuration. In accordance withone embodiment, programmable parameters, their ranges, and nominalvalues are:

Parameter Min Max Nominal Amplitude 0 mA 7.0 mA 1 mA Pulse Width 25 μs500 μs 200 μs Rate 1 Hz 40 Hz 20 Hz On Ramp 0 s 5 s 2 s Off RampCycle-On 2 s 20 s 10 s Cycle-Off 20 s 120 s 20 s Session 1 min 60 min 30min

Controller 318 may be programmable to allow electrical stimulationbetween any chosen combination of electrodes on the lead, thus providinga simple bipolar configuration. In addition, controller 318 may beprogrammed to deliver stimulation pulses in a guarded bipolarconfiguration (more than 1 anode surrounding a central cathode) or thehousing of IPG 300 may be programmed as the anode, enabling unipolarstimulation from any of the electrodes. IPG 300 may have two separatechannels to facilitate bilateral stimulation and the electrodeconfiguration, e.g., combination of positive and negative electrodes,may be programmed independently for each channel.

As will be appreciated by one of ordinary skill in the art, while IPG300 is illustratively implantable, a pulse generator may be disposedexternal to a body of a patient on a temporary or permanent basiswithout departing from the scope of the present invention. For example,an external stimulator may be coupled to the electrodes wirelessly.

Controller 318 further may be programmed with a routine to calculate theimpedance at electrode lead 200. For example, controller 318 may directpower supply 324 to send an electrical signal to one or more electrodeswhich emit electrical power. One or more other electrodes receive theemitted electrical power and send a received signal to controller 318that runs the routine to calculate impedance based on the sent signaland the received signal. The impedance measurement may be used todetermine whether one or more of the fixation elements coupled to theelectrode lead body are in a delivery state or a deployed state. In oneembodiment, controller 318 directs electrode 210 to emit energy suchthat electrode 204, 206, or 208 receives a portion of the emitted energyand sends a received signal to controller 318. Also, controller 318 maydirect electrode 204, 206, or 208 to emit energy such that electrode 210receives a portion of the emitted energy and sends a received signal tocontroller 318. Controller 318 runs the routine to calculate impedancebased on the signal having data indicative of emitted energy and thesignal having data indicative of received energy to determine animpedance measurement. Advantageously, the proximity of the fixationelement(s) to the electrode(s) will change the impedance measured at theelectrode(s) as the resistance of the electrical energy travelingbetween electrodes increases as the angle between the fixationelement(s) and the electrode(s) decreases. For example, the resistanceof electrical energy traveling between electrode 210 and electrode 204,206, or 208 may be higher in the delivery state than in the deployedstate.

Controller 318 causes communication unit 320 to transmit a signalindicative of the impedance measurement to the external computer runningsoftware 600, e.g., via external programmer 500. A physician may reviewthe impedance measurement on software 600 to determine whether one ormore fixation elements are in the deployed or the delivery state. If thephysician determines that one or more of the fixation elements are inthe delivery state after retraction of a sheath, the physician mayadjust the lead in an attempt to cause the non-deployed fixationelement(s) to deploy. Then, the physician may request a second impedancemeasurement using software 600. The external computer transmits thecommand, e.g., via external programmer 500, to IPG 300 and controller318 repeats the steps to calculate impedance. Controller 318 thendirects communication unit 320 to transmit a second signal indicative ofthe second impedance measurement to the external computer runningsoftware 600, e.g., via external programmer 500. The physician maydetermine whether one or more fixation elements have deployed based onthe second impedance measurement. The physician may continue to adjustthe lead and request impedance measurements as necessary until thephysician is satisfied that the fixation elements have deployed.

Controller 318 is coupled to communication unit 320 having circuitryconfigured to communicate with activator 400 and the external computer,e.g., via external programmer 500. Communication unit 320 permitstransmission of stimulation commands, and optionally power, between IPG300 and activator 400 such that IPG 300 may be powered, programmed,and/or controlled by activator 400. For example, controller 318 maystart or stop a treatment session or to conduct an impedance assessmentresponsive to stimulation commands received from a correspondingcommunication unit (e.g., an inductive unit having a telemetry systemand coil and/or a RF unit having a transceiver and antenna) of activator400. Communication unit 320 further permits transmission of programmingdata, and optionally power, between IPG 300 and external programmer 500such that IPG 300 may be powered, programmed, and/or controlled bysoftware-based programming system 600 via external programmer 500. Forexample, controller 318 may direct changes to at least one of pulseamplitude (voltage or current), pulse width, stimulation rate,stimulation frequency, ramp timing, cycle timing, session timing, andelectrode configuration and to conduct an impedance assessmentresponsive to programming data received from a correspondingcommunication unit (e.g., an inductive unit having a telemetry systemand coil and/or a RF unit having a transceiver and antenna) of externalprogrammer 500.

Communication unit 320 may include a telemetry system electricallycoupled to an inductive coil. The technology for telemetry systems andcoils is well known to one skilled in the art and may include a magnet,a short range telemetry system, a longer range telemetry system (such asusing MICS RF Telemetry available from Zarlink Semiconductor of Ottawa,Canada), or technology similar to a pacemaker programmer. Alternatively,the coil may be used to transmit power only, and separate radiofrequency transmitters may be provided in IPG 300 activator 400, and/orexternal programmer 500 for establishing bidirectional or unidirectionaldata communication.

Communication unit 320 also may include (with or without the telemetrysystem and coil) a communications circuit employing a transceivercoupled to an antenna 334 (which may be inside or external to thehermetic housing). The transceiver preferably comprises a radiofrequency (RF) transceiver and is configured for bi-directionalcommunications via the antenna with a similar transceiver circuitdisposed in activator 400 and/or external programmer 500. For example,the transceiver may receive stimulation commands from activator 400 andprogramming data from software-based programming system 600 via externalprogrammer 500. Controller 318 may direct changes to at least one ofpulse amplitude (voltage or current), pulse width, stimulation rate,stimulation frequency, ramp timing, cycle timing, session timing, andelectrode configuration, including commands to start or stop a treatmentsession or to conduct impedance assessment, responsive to programmingdata and/or stimulation commands received from a correspondingtransceiver and antenna of activator 400 and/or external programmer 500via the antenna and the transceiver of communication unit 320. Thetransceiver also may include a low power mode of operation, such that itperiodically awakens to listen for incoming messages and responds onlyto those messages including the unique device identifier assigned tothat IPG. In addition, the transceiver may employ an encryption routineto ensure that messages sent from, or received by, IPG 300 cannot beintercepted or forged. Communication unit 320 may include a wirelesschipset, e.g., WiFi, Bluetooth, cellular, thereby enabling IPG 300 tocommunicate wirelessly with activator 400, external programmer 500,and/or the external computer running software 600.

Power supply 324 powers the electrical components of IPG 300, and maycomprise a primary cell or battery, a secondary (rechargeable) cell orbattery or a combination of both. Alternatively, power supply 324 maynot include a cell or battery, but instead comprise a capacitor thatstores energy transmitted through the skin via a Transcutaneous EnergyTransmission System (TETs), e.g., by inductive coupling. In a preferredembodiment, power supply 324 comprises a lithium ion battery.

Controller 318 further may be coupled to electrode switching array 326so that any subset of electrodes of the electrode leads may beselectably coupled to therapeutic circuitry module 330, described indetail below. In this way, an appropriate electrode set may be chosenfrom the entire selection of electrodes implanted in the patient's bodyto achieve a desired therapeutic effect. Electrode switching array 326preferably operates at high speed, thereby allowing successivestimulation pulses to be applied to different electrode combinations.

System sensors 328 may comprise one or more sensors that monitoroperation of the systems of IPG 300, and log data relating to systemoperation as well as system faults, which may be stored in a log forlater readout using software-based programming system 600. In oneembodiment, system sensors 328 include a magnetic sensor configured tosense a magnetic field and to transmit a signal to controller 318 basedon the sensed magnetic field such that the controller starts or stops atreatment session. In another embodiment, system sensors 328 include oneor more sensors configured to sense muscle contraction and to generate asensor signal based on the muscle contraction. Controller 318 isconfigured to receive the sensor signal from system sensors 328 and toadjust the stimulation parameters based on the sensor signal. In oneembodiment, system sensors 328 sense an increase or decrease in musclemovement and controller 318 increases or decreases the stimulationfrequency to maintain smooth and continuous muscle contraction.

In one embodiment, sensors 328 may include an accelerometer that sensesacceleration of a muscle caused by muscle contraction. The accelerometermay be a 1-, 2- or 3-axis analog or digital accelerometer thatdetermines whether the patient is active or asleep or senses overallactivity of the patient, which may be a surrogate measure for clinicalparameters (e.g., more activity implies less pain), and/or a heart rateor breathing rate (minute ventilation) monitor, e.g., which may beobtained using one or more of the electrodes disposed on the electrodeleads. The accelerometer may be used to determine the orientation of IPG300, and by inference the orientation of the patient, at any time. Forexample, after implantation, software-based programming system 600 maybe used to take a reading from the implant, e.g., when the patient islying prone, to calibrate the orientation of the accelerometer. If thepatient is instructed to lie prone during therapy delivery, then theaccelerometer may be programmed to record the orientation of the patientduring stimulation, thus providing information on patient compliance. Inother embodiments, system sensors 328 may include a pressure sensor, amovement sensor, and/or a strain gauge configured to sense musclecontraction and to generate a sensor signal based on the musclecontraction, and in a further embodiment, various combinations of atleast one of an accelerometer, a pressure sensor, a movement sensor,and/or a strain gauge are included.

Sensors 328 may also include, for example, a humidity sensor to measuremoisture within housing 304, which may provide information relating tothe state of the electronic components, or a temperature sensor, e.g.,for measuring battery temperature during charging to ensure safeoperation of the battery. Data from the system sensors may be logged bycontroller 318 and stored in nonvolatile memory for later transmissionto software-based programming system 600 via external programmer 500.

As will be appreciated by one of ordinary skill in the art, systemsensors 328 may be placed in a variety of locations including withinhousing 302, within or adjacent to the tissue that is stimulated, and/orin proximity to the muscle to be contracted and connected via a separatelead to IPG 300. In other embodiments, sensors 324 may be integratedinto one or more of the leads used for stimulation or may be anindependent sensor(s) operatively coupled to IPG 300 using, for example,radio frequency (RF) signals for transmitting and receiving data.

Controller 318 also may be coupled to optional therapeutic circuitrymodule 330 that provides any of a number of complimentary therapeuticstimulation, analgesic, feedback or ablation treatment modalities asdescribed in detail below. IPG 300 illustratively includes onetherapeutic circuitry module 330, although additional circuitry modulesmay be employed in a particular embodiment depending upon its intendedapplication, as described in U.S. Patent Application Publication No.2011/0224665 to Crosby, assigned to the assignee of the presentinvention, the entire contents of which is incorporated herein byreference. Therapeutic circuitry module 330 may be configured to providedifferent types of stimulation, either to induce muscle contractions orto block pain signals in afferent nerve fibers; to monitor musclecontractions induced by stimulation and adjust the applied stimulationregime as needed to obtain a desired result; or to selectively andintermittently ablate nerve fibers to control pain and therebyfacilitate muscle rehabilitation.

Referring now to FIG. 4, kit 700 for delivering electrode lead 200 isdescribed, including suture sleeve 701, needle electrode 702, and sheath704. In FIG. 4, components of the kit are not depicted to scale oneither a relative or absolute basis. Suture sleeve 701 illustrativelyincludes first end section 706, middle section 708 separated from firstend section by first groove 710, second end section 712 separated frommiddle section 708 by second groove 714, and sleeve lumen 716. First andsecond end sections 706 and 712 may have truncated conical portions asshown. First and second grooves 710 and 714 are sized and shaped toaccept sutures such that suture sleeve 701 may be secured to tissue,e.g., superficial fascia, using the sutures. Sleeve lumen 716 is sizedsuch that electrode lead 200 may be inserted therethrough.

Needle electrode 702 may include distal tip 718, radiopaque marker 720,electrodes 722, 724 disposed near distal tip 718, and connector 726.Distal tip 718, radiopaque marker 720, and electrodes 722, 724 arelocated at distal end 725 of needle electrode 702. Distal tip 718 isshaped with a needle point to facilitate insertion of needle electrode702 through tissue to the target site. Alternatively, distal tip 718 mayhave a blunt end to minimize tissue damage during insertion and toseparate anatomical structures along naturally occurring tissue planes.Radiopaque marker 720 is configured to permit visualization of needleelectrode 702 under fluoroscopic, acoustic, anatomic, or CT guidanceduring insertion. Electrodes 722, 724 are configured to emit energy tostimulate tissue. As will be understood by one of skill in the art, aneedle electrode may contain more or fewer than two electrodes and morethan one radiopaque marker.

Needle electrode 702 may be coupled to processor housing 750, e.g., viaconnector 726. Alternatively, needle electrode 702 may be coupleddirectly to an external computer such as the computer running software600, e.g., via connector 726. Processor housing 750 houses circuitryconfigured to cause electrodes 722, 724 emit energy responsive to userinput at the housing itself or at the computer running software 600.Processor housing 750 may be coupled to a computer, such as the computerrunning software 600, via cable 728 and connector 730.

Sheath 704 may include sheath lumen 732, distal tip 734, radiopaquemarker 736, windows 738, 740 near distal tip 734, coupling portion 742,and handle 744. Distal tip 734, radiopaque marker 736, and windows 738,740 are located at distal end 741 of sheath 704. Sheath lumen 732extends through sheath 704 and is shaped and sized to permit needleelectrode 702 to slide therethrough. Distal tip 734 is beveled to easeintroduction through tissue. Radiopaque marker 736 is configured topermit visualization of sheath 704 under fluoroscopic, acoustic,anatomic, or CT guidance during insertion. Windows are configured topermit energy emitted from electrodes disposed within sheath 704 totravel therethrough while the electrodes remain within the sheath.Accordingly, the electrodes, e.g., electrodes on electrode lead 200 orneedle electrode 702, need not extend out the distal end of sheath 704to stimulate tissue. Advantageously, proper positioning of theelectrodes may be verified while the electrodes remain within sheath 704minimizing the likelihood of needing to adjust electrode position afterdeployment, including deployment of a fixation element(s). Couplingportion 742, illustratively a male end with threads, is configured to becoupled to a portion of needle electrode 702. Handle 744 is sized andshaped to permit a physician to comfortably hold sheath 704. As will beunderstood by one of skill in the art, a sheath may contain more orfewer than two windows and more than one radiopaque marker.

With respect to FIG. 5, a generalized schematic diagram of the internalfunctional components of processor housing 750 is now described.Processor housing 750 may include programmable controller 752,communication unit 754, user interface 756, power supply 758, and inputand output circuitry (I/O) 760.

Controller 752 is electrically coupled to, and configured to control,the internal functional components of processor housing 750. Controller752 may comprise a commercially available microcontroller unit includinga programmable microprocessor, volatile memory, nonvolatile memory suchas EEPROM for storing programming, and nonvolatile storage, e.g., Flashmemory, for storing firmware and a log of system operational parametersand patient data. The memory of controller 752 may store programinstructions that, when executed by the processor of controller 752,cause the processor and the functional components of processor housing750 to provide the functionality ascribed to them herein. Controller 752is configured to be programmable. For example, controller 752 may storeand adjust stimulation parameters, e.g., pulse amplitude (voltage orcurrent), pulse width, stimulation rate, stimulation frequency, ramptiming, cycle timing, session timing, and electrode configurationresponsive to user input received at user interface 756 or at anexternal computer such as the computer running software 600.

Controller 752 may be coupled to communication unit 754, which isconfigured to communicate with an external computer, such as thecomputer running software 600. Communication unit 754 may include awireless chipset, e.g., WiFi, Bluetooth, cellular, thereby enablingprocessor housing 750 to communicate wirelessly with external programmer500 and/or the external computer running software 600.

User interface 756 is configured to receive user input and to displayinformation to the user. User interface 756 may include buttons, LEDs, adisplay, a touch screen, a keypad, a microphone, a speaker, a trackball,or the like for receiving user input and/or displaying information tothe user. For example, user interface 756 may display currentstimulation parameters and permit a user to adjust the stimulationparameters. User interface 756 also may permit a user to cause one ormore electrodes 722, 724 to emit energy.

Power supply 758 powers the electrical components of processor housing750, and may comprise a primary cell or battery, a secondary(rechargeable) cell or battery or a combination of both. Alternatively,power supply 758 may be a port to allow processor housing 750 to beplugged into a conventional wall socket for powering components.Controller 752 may direct power supply 758 to send an electrical signalto one or more electrodes 722, 724 which emit electrical energy at thestimulation parameters programmed in controller 752.

Input and output circuitry (I/O) 760 may include ports for datacommunication such as wired communication with a computer and/or portsfor receiving removable memory, e.g., SD card, upon which programinstructions or data related to processor housing 750 use may be stored.In one embodiment, I/O 760 includes a port for connection to needleelectrode 702 via connector 726 and another port for accepting cable 728which may be connected to an external computer.

Referring now to FIGS. 6A to 6F, an exemplary method for implanting anelectrode lead is described. Using fluoroscopy, acoustic, anatomic, orCT guidance, needle electrode 702 and sheath 704 are insertedtranscutaneously and transmuscularly to a target site, e.g., in oradjacent to tissue associated with control of the lumbar spine.Preferably, distal end 725 of needle electrode 702 is positioned in oradjacent to the tissue, as shown in FIG. 6A. Such tissue may includenervous tissue, muscle, ligament, and/or joint capsule. In oneembodiment, muscle includes skeletal muscle such as the multifidus,transverse abdominus, quadratus lumborum, psoas major, internusabdominus, obliquus externus abdominus, and erector spinae muscles andnervous tissue includes a peripheral nerve that innervates skeletalmuscle. In a preferred embodiment, nervous tissue comprises the dorsalramus nerve, or fascicles thereof, that innervate the multifidus muscle.Preferably, needle electrode 702 is disposed within sheath lumen 732prior to insertion such that needle electrode 702 and sheath 704 areinserted together. Advantageously, a guidewire need not be delivered (i)prior to insertion of needle electrode 702 or sheath 704, (ii) throughneedle electrode 702 or sheath 704 during insertion, or (iii) throughneedle electrode 702 or sheath 704 after insertion.

FIGS. 6A-6F depict a lateral projection of a segment of a typical humanlumbar spine shown having a vertebral body V, transverse process TP,inter-transverse ligament ITL, and a dorsal ramus DR. In FIG. 6A, sheath704 having needle electrode 702 disposed therethrough, is positionedadjacent to the target site, illustratively, the medial branch of thedorsal ramus DR nerve that innervates the multifidus muscle. Distal tip718 of needle electrode 702 may extend out of the distal end of sheath704 to facilitate insertion through tissue. In one embodiment,electrodes of the electrode lead are positioned to stimulate the medialbranch of the dorsal ramus that exits between the L2 and L3 lumbarsegments and passes over the transverse process of the L3 vertebra,thereby eliciting contraction of fascicles of the lumbar multifidus atthe L3, L4, L5 and 51 segments and in some patients also at the L2segment.

Next, needle electrode 702 stimulates the tissue. Preferably, electrode722 and/or electrode 724 stimulates the tissue at the stimulationparameters defined at processor housing 750. In an embodiment wheresheath 704 has windows 738, 740, electrodes 722, 724 of needle electrode702 emit energy through windows 738, 740 while electrodes 722, 724remain within sheath 704. Preferably, windows 738, 740 are sized andspaced with the same or similar dimensions to the length and spacing ofelectrodes 722, 724 of needle electrode 702 and/or electrodes 204, 206,208, 210 of electrode lead 200. In this way, the electrodes are morelikely to be aligned with the windows while disposed within the patient.In addition, radiopaque markers 720, 736 of needle electrode 702, sheath704, respectively, may be positioned such that electrodes 722, 724 alignwithin windows 738, 740, respectively, when radiopaque markers 720, 736are aligned. Similarly, a radiopaque marker(s) may be disposed onelectrode lead 200 to facilitate alignment of electrodes 204, 206, 208,210 within the windows of the sheath. In one embodiment, one or morefixation elements 212, 213, 214, 215 has a radiopaque marker(s) toassist in visualization under fluoroscopic, acoustic, anatomic, or CTguidance to determine whether one or more of the fixation elements arein the delivery state or the deployed state.

Alternatively, or additionally, distal end 725 of needle electrode 702may be moved distally out of the distal end of sheath 704 whilemaintaining position of sheath 704 (or sheath 704 moved proximally,e.g., using handle 744, while maintaining position of needle electrode702), thereby exposing electrodes 722, 724, as shown in FIG. 6B. Such astep may be useful in embodiments where the sheath does not havewindows. Once exposed, needle electrode 702 stimulates the tissue.Preferably, electrode 722 and/or electrode 724 stimulates the tissue atthe stimulation parameters defined at processor housing 750.

By stimulating the tissue, proper placement of needle electrode 702 andsheath 704 may be verified. For example, using fluoroscopy, acoustic,anatomic, or CT imaging, a physician may verify that the target musclecontracts responsive to the stimulation. If the target muscle does notcontract, or does not contract in a suitable manner, the physician mayadjust placement of needle electrode 702 and/or sheath 704, e.g., bymoving needle electrode 702 and/or sheath 704 proximally or distally.The physician may continue to make adjustments until suitable placementof needle electrode 702 and/or sheath 704 has been verified.

After verification, needle electrode 702 is removed from sheath 704while maintaining position of sheath 704 at the target site. Usingfluoroscopy, acoustic, anatomic, or CT guidance, electrode lead 200 isinserted through sheath lumen 732 of sheath 704 to position electrodes204, 206, 208, 210 at the target site, as shown in FIG. 6C. As describedabove, a radiopaque marker on electrode lead 200 may be aligned withradiopaque marker 736 of sheath 704 to ensure that distal end 211 ofelectrode lead 200 is at distal end 741 of sheath 704, and optionally,that the electrodes of electrode lead 200 are aligned within respectivewindows of sheath 704. Advantageously, a guidewire need not be delivered(i) prior to insertion of electrode lead 200, (ii) through electrodelead 200 during insertion, or (iii) through electrode lead 200 afterinsertion.

A stylet may be inserted within the stylet lumen of electrode lead 200to provide additional stiffness to electrode lead 200 to ease passage ofelectrode lead 200 through sheath 704. The stylet may be a commerciallyavailable stylet such as a locking stylet available from Cook GroupIncorporated of Bloomington, Ind.

Next, electrode lead 200 stimulates the tissue. Preferably, electrode204, 206, 208 and/or electrode 210 stimulates the tissue at thestimulation parameters defined at a pulse generator, such as IPG 300,coupled to the electrodes. In an embodiment where sheath 704 has windows738, 740, electrodes 210, 208 of electrode lead 200 emit energy throughwindows 738, 740, respectively, while electrodes 210, 208 remain withinsheath 704. As will be understood by one of skill in the art, a sheathmay contain more or fewer than two windows. For example, sheath 704 mayhave four windows sized and shaped to align with electrodes 204, 206,208, 210 of electrode lead. Advantageously, proper positioning of theelectrodes may be verified while the electrodes remain within sheath 704minimizing the likelihood of needing to adjust electrode position afterdeployment, including deployment of a fixation element(s) on electrodelead 200.

Alternatively, or additionally, distal end 211 of electrode lead 200 maybe moved distally out of the distal end of sheath 704 while maintainingposition of sheath 704 (or sheath 704 moved proximally, e.g., usinghandle 744, while maintaining position of electrode lead 200), therebyexposing one or more electrodes 204, 206, 208, and/or 210, as shown inFIGS. 6D and 6E. Such a step may be useful in embodiments where thesheath does not have windows. After electrode exposure, electrode lead200 stimulates the tissue. Preferably, electrode 204, 206, 208 and/orelectrode 210 stimulates the tissue at the stimulation parametersdefined at a pulse generator, such as IPG 300, coupled to theelectrodes.

By stimulating the tissue, proper placement of electrode lead 200 may beverified, and specifically placement of electrodes 204, 206, 208, 210 atdistal end 211 may be verified. For example, using fluoroscopy,acoustic, anatomic, or CT imaging, a physician may verify that thetarget muscle contracts responsive to the stimulation. If the targetmuscle does not contract, or does not contract in a suitable manner, thephysician may adjust placement of electrode lead 200 and/or sheath 704,e.g., by moving electrode lead 200 and/or sheath 704 proximally ordistally. The physician may continue to make adjustments until suitableplacement of electrode lead 200 has been verified.

Preferably, fixation elements 212, 213, 214, 215 individually transitionfrom a collapsed, delivery state within sheath 704 to an expanded,deployed state, shown in FIG. 6E, as the respective fixation element isexposed out of the distal end of sheath 704. The fixation elementssandwich an anchor site, e.g., muscle, therebetween without damaging theanchor site in the expanded state to fix electrode lead 200 at thetarget site. However, it is contemplated that one or more fixationelements 212, 213, 214, 215 may not expand to the deployed state, asshown in FIG. 6D.

A method for verifying deployment of one or more fixation elements isnow described. After implantation of electrode lead 200 at the targetsite as described above, electrode lead 200 stimulates the tissue.Preferably, electrode 204, 206, 208 and/or electrode 210 stimulates thetissue at the stimulation parameters responsive to a signal sent by apulse generator, such as IPG 300, coupled to the electrodes. One or moreother electrodes receive the emitted electrical power and send areceived signal to the controller of the pulse generator that runs theroutine to calculate impedance based on the sent signal and the receivedsignal. The impedance measurement may be used to determine whether oneor more fixation elements 212, 213, 214, 215 are in a delivery state ora deployed state. In one embodiment, the pulse generator directselectrode 210 to emit energy such that electrode 204, 206, or 208receives a portion of the emitted energy and sends a received signal tothe pulse generator. Also, the pulse generator may direct electrode 204,206, or 208 to emit energy such that electrode 210 receives a portion ofthe emitted energy and sends a received signal to the pulse generator.The pulse generator runs the routine to calculate impedance based on thesignal having data indicative of emitted energy and the signal havingdata indicative of received energy to determine an impedancemeasurement. Advantageously, the proximity of the fixation element(s) tothe electrode(s) will change the impedance measured at the electrode(s)as the resistance of the electrical energy traveling between electrodesincreases as the angle between the fixation element(s) and theelectrode(s) decreases. For example, the resistance of electrical energytraveling between electrode 210 and electrode 204, 206, or 208 may behigher in the delivery state than in the deployed state.

The pulse generator transmits a signal indicative of the impedancemeasurement to the external computer running software 600, e.g., viaexternal programmer 500. A physician may review the impedancemeasurement on software 600 to determine whether one or more fixationelements 212, 213, 214, 215 are in the deployed or the delivery state.If the physician determines that one or more fixation elements 212, 213,214, 215 are in the delivery state after retraction of a sheath (as isshown in FIG. 6D), the physician may adjust electrode lead 200 in anattempt to cause the non-deployed fixation element(s) to deploy, e.g.,move electrode lead 200 proximally and/or distally. Then, the physicianmay request a second impedance measurement using software 600. Theexternal computer transmits the command, e.g., via external programmer500, to the pulse generator which repeats the steps to calculateimpedance. The pulse generator then transmits a second signal indicativeof the second impedance measurement to the external computer runningsoftware 600, e.g., via external programmer 500. The physician maydetermine whether one or more fixation elements 212, 213, 214, 215 havedeployed based on the second impedance measurement. The physician maycontinue to adjust electrode lead 200 and request impedance measurementsas necessary until the physician is satisfied that fixation elements212, 213, 214, 215 have all deployed.

In one embodiment, software 600 is configured to determine if thefixation element(s) is deployed and, preferably, how many fixationelements have deployed. For example, software 600 may process theimpedance measurement to determine whether a fixation element(s) isdeployed using a lookup table having stored impedance value rangescorresponding to the number of fixation elements deployed. Software 600may cause the computer running software 600 to display a messagereflecting the number of fixation elements deployed and/or reflectingsuitable/unsuitable deployment of the fixation elements.

After verification that electrode lead 200 is suitably positioned withinthe patient at the target site, and preferably after verification thatthe fixation element(s) is deployed, sheath 704 is moved proximally offthe proximal end of electrode lead 200 and suture sleeve 701 is placedover the proximal end of electrode lead 200 and moved distally, asillustrated in FIG. 6F. When suture sleeve 701 is positioned adjacent tothe superficial fascia SF beneath skin SK, sutures are sewn into thefirst and second grooves of suture sleeve 701 so as to secure suturesleeve 701 to the superficial fascia SF.

Finally, the IPG is coupled to the proximal end of electrode lead 200and implanted within the lower back of the patient.

Exemplary stimulation parameters are now described. Preferably, suchstimulation parameters are selected and programmed to induce contractionof muscle to restore neural control and rehabilitate muscle associatedwith control of the spine, thereby improving lumbar spine stability andreducing back pain. As used in this specification, “to restore musclefunction” means to restore an observable degree of muscle function asrecognized by existing measures of patient assessment, such as theOswestry Disability Index (“ODI”) as described in Lauridsen et al.,Responsiveness and minimal clinically important difference for pain anddisability instruments in low back pain patients, BMC MusculoskeletalDisorders, 7: 82-97 (2006), the European Quality of Life Assessment 5D(“EQ-5D”) as described in Brazier et al., A comparison of the EQ-5D andSF-6D across seven patient groups, Health Econ. 13: 873-884 (2004), or aVisual Analogue Scale (“VAS”) as described in Hagg et al., The clinicalimportance of changes in outcome scores after treatment for chronic lowback pain, Eur Spine J 12: 12-20 (2003). In accordance with one aspectof the present invention, “to restore muscle function” means to observeat least a 15% improvement in one of the foregoing assessment scoreswithin 30-60 days of initiation of treatment. As described above, thestimulation parameters may be programmed into the IPG, may be adjustedin the IPG responsive to (i) stimulation commands transferred from theactivator or (ii) programming data transferred from the externalprogrammer.

The stimulation parameters include, for example, pulse amplitude(voltage or current), pulse width, stimulation rate, stimulationfrequency, ramp timing, cycle timing, session timing, and electrodeconfiguration, including commands to start or stop a treatment session.In one embodiment, pulse amplitude is programmed to be adjustablebetween 0 and 7 mA. In a preferred embodiment, pulse amplitude isprogrammed to be between about 2-5 mA, 2.5-4.5 mA, or 3-4 mA, andpreferably about 3.5 mA. In one embodiment, pulse width is programmed tobe adjustable between 25 and 500 μs. In a preferred embodiment, pulsewidth is programmed to be between about 100-400 μs, 150-350 μs, or200-300 μs, and preferably about 350 μs. In one embodiment, stimulationrate is programmed to be adjustable between 1 and 40 Hz. In a preferredembodiment, stimulation rate is programmed to be between about 5-35 Hz,10-30 Hz, or 15-20 Hz, and preferably about 20 Hz. In one embodiment, onramp timing is programmed to be adjustable between 0 and 5 s. In apreferred embodiment, on ramp timing is programmed to be between about0.5-4.5 s, 1-4 s, 1.5-3.5 s, or 2-3 s, and preferably about 2.5 s. Inone embodiment, off ramp timing is programmed to be adjustable between 0and 5 s. In a preferred embodiment, off ramp timing is programmed to bebetween about 0.5-4.5 s, 1-4 s, 1.5-3.5 s, or 2-3 s, and preferablyabout 2.5 s. In one embodiment, cycle-on timing is programmed to beadjustable between 2 and 20 s. In a preferred embodiment, cycle-ontiming is programmed to be between about 4-18 s, 6-16 s, 8-14 s, 9-13 s,or 10-12 s and preferably about 10 s. In one embodiment, cycle-offtiming is programmed to be adjustable between 20 and 120 s. In apreferred embodiment, cycle-off timing is programmed to be between about30-110 s, 40-100 s, 50-90 s, 55-85 s, 60-80 s, or 65-75 s and preferablyabout 70 s. In one embodiment, session timing is programmed to beadjustable between 1 and 60 min. In a preferred embodiment, sessiontiming is programmed to be between about 5-55 min, 10-50 min, 15-45 min,20-40 min, or 25-35 min, and preferably about 30 min.

Referring now to FIG. 7, an exemplary graphical user interface ofsoftware 600 is described for a stimulator system. FIG. 7 showsimpedance screen 800 that is displayed to a physician runningsoftware-based programming system 600. Impedance screen 800 includeselectrode configuration area 802 and impedance matrix area 804.

Electrode configuration area 802 includes right electrode lead impedancedisplay, left electrode lead impedance display, and Impedance area.Right electrode lead impedance display shows an illustration of fourelectrodes (numbered 5-8) on the right electrode lead implanted withinthe subject while left electrode lead impedance display shows the fourelectrodes (numbered 1-4) on the left electrode lead implanted withinthe subject. A user may select at which electrode(s) to measureimpedance using the respective displays and may change the polarity ofeach electrode between positive and negative. In the illustratedembodiment, when a session begins, negative electrode 6 on the rightlead and negative electrode 2 on the left lead transmit energy to targettissue to stimulate the tissue and positive electrodes 5 and 1,respectively, receive the energy after it has passed through the targettissue.

Impedance area permits a user to select the “Measure Impedance” buttonwhich causes the programming system, e.g., via the external programmer,to command the pulse generator to run the routine to measure impedancesand then transmit the measured impedances back to the programmingsystem, e.g., via the external programmer. The measured impedances thenare displayed for each electrode. As described above, the displayedimpedance may be used to determine whether one or more fixation elementson the electrode lead are deployed.

Impedance matrix area 804 includes an impedance matrix and a “MeasureImpedance Matrix” button. When pressed, the “Measure Impedance Matrix”button causes the impedance matrix to be populated with the measuredimpedances in accordance with selections made at electrode configurationarea 802. The impedance matrix is populated with the impedance measuredbetween two select electrodes having opposite polarities during theimpedance assessment, e.g., based on electrode activation and polarityselected at left electrode lead impedance display and right electrodelead impedance display. The displayed impedances in the impedance matrixmay be used to determine whether one or more fixation elements on theelectrode lead are deployed. In addition, the impedance measurements maybe time stamped. If an electrode shorts out, the IPG may be configuredto exclude the nonfunctioning electrode and the time stamp may be usedto determine when the electrode shorted out.

In the illustrated embodiment, impedance between electrode 2 (selectedto be negative) and electrode 1 (selected to be positive) on the leftlead is measured to be 490 Ohms and impedance between electrode 6(selected to be negative) and electrode 5 (selected to be positive) onthe right electrode lead is measured to be 1355 Ohms. Thus, when theMeasure Impedance Matrix button is pressed, the software causes 490 tobe populated at the intersection of 2 negative and 1 positive and 1355to be populated at the intersection of 6 negative and 5 positive in theimpedance matrix. The impedance matrix also may display when anelectrode is excluded or out of range.

As will be readily understood by one of ordinary skill in the art, auser may enter data into the graphical user interface using suitablemechanisms known in the art, such as, entering numbers, letters, and/orsymbols via a keyboard or touch screen, mouse, touchpad, selection froma drop-down menu, voice commands, or the like.

While various illustrative embodiments of the invention are describedabove, it will be apparent to one skilled in the art that variouschanges and modifications may be made therein without departing from theinvention. The appended claims are intended to cover all such changesand modifications that fall within the true scope of the invention.

What is claimed:
 1. A system for restoring muscle function to the lumbarspine, the system comprising: first and second electrodes configured tobe implanted in or adjacent to tissue associated with control of thelumbar spine; a lead having the first and second electrodes disposedthereon; a fixation element coupled to the lead and disposed inproximity to the first electrode, the fixation element configured totransition from a delivery state, wherein the fixation element ispositioned adjacent to the first electrode, to a deployed state, whereinthe fixation element is spaced apart from the first electrode and ispositioned to anchor the lead to an anchor site; a pulse generatorcoupled to the first and second electrodes via the lead, the pulsegenerator configured to cause the first or second electrode to emitenergy such that the second or first electrode, respectively, receives aportion of the emitted energy, the pulse generator further configured totransmit a signal indicative of an impedance measurement based on theenergy emitted and the portion of the energy received; and softwarestored on a non-transient computer readable media configured to run onan external computer operatively coupled to the pulse generator, thesoftware configured to cause the external computer to display theimpedance measurement and to indicate whether the fixation element is inthe delivery state or the deployed state based on the impedancemeasurement.
 2. The system of claim 1, further comprising a secondfixation element coupled to the lead distal to the fixation element,wherein the fixation element is angled distally relative to the lead andthe second fixation element is angled proximally relative to the lead,and wherein the fixation element and the second fixation element areconfigured to sandwich the anchor site therebetween.
 3. The system ofclaim 1, further comprising an external programmer coupled to theexternal computer, the external programmer configured to receive thesignal indicative of the impedance measurement from the pulse generatorand to transmit the signal to the external computer.
 4. The system ofclaim 3, wherein the external programmer is configured to transferprogramming data to the pulse generator.
 5. The system of claim 4,wherein the software is configured to permit selection, adjustment, anddisplay of the programming data.
 6. The system of claim 4, wherein theprogramming data comprises at least one of: pulse amplitude, pulsewidth, stimulation rate, stimulation frequency, ramp timing, cycletiming, session timing, or electrode configuration.
 7. The system ofclaim 4, further comprising a handheld activator configured to transfera stimulation command to the pulse generator, wherein the stimulationcommand directs at least one of the first or second electrodes tostimulate the tissue in accordance with the programming data.
 8. Thesystem of claim 1, wherein the software is further configured to causethe external computer to display a second impedance measurement based ona second signal.
 9. The system of claim 1, wherein the software isconfigured to determine whether the fixation element is in the deliverystate or the deployed state.
 10. The system of claim 1, wherein theimpedance measurement is indicative of the fixation element being in thedelivery state in a range and the impedance measurement is indicative ofthe fixation element being in the deployed state in a different range.11. The system of claim 10, wherein the range is between 1501-3500 ohms,1200-2500 ohms, 1000-2000 ohms, or 750-1750 ohms and the different rangeis between 500-1500 ohms, 500-1200 ohms, 500-1000 ohms, or 500-750 ohms.12. A method of verifying deployment of a fixation element in a systemfor restoring muscle function to the lumbar spine, the methodcomprising: implanting a lead such that an electrode disposed on thelead is positioned in or adjacent to tissue associated with control ofthe lumbar spine, the lead coupled to a fixation element disposed inproximity to the electrode, the fixation element configured totransition from a delivery state, wherein the fixation element ispositioned adjacent to the electrode, to a deployed state, wherein thefixation element is spaced apart from the electrode and is positioned toanchor the lead to an anchor site; causing the electrode to stimulatetissue using a pulse generator; transmitting a signal indicative of animpedance measurement to an external display; displaying the impedancemeasurement on the external display; and determining whether thefixation element is in the delivery state or the deployed state based onthe displayed impedance measurement.
 13. The method of claim 12, whereinthe signal is transmitted from the pulse generator to an externalprogrammer coupled to an external computer having the external display.14. The method of claim 12, further comprising adjusting the lead if thefixation element is determined to be in the delivery state.